Calling between servers

[Brian]

So my 2 accounts (I'm talking accounts, not 2 lines on 1 account) have, in the past, been set to register to different servers. When they are set to different servers, I get a busy signal when calling between them (at least some of the time, depending on which way I'm calling - I think sip to east). I've put in a ticket with support, and they had me update the lines so they're both registering to the same server, and all is good. My question - why is calling from VOIPo to VOIPo server-dependent? Shouldn't I be able to register to any VOIPo server and call an account on another?

[usa2k]

Curious which devices you have?

[Brian]

I just got my replacement PAP2, and it happened when I used that (2 PAP2's), and it happened when my main number was on a GS, and 2nd was on a PAP2.